[LAD] mixing while using libao and libsndfile
dave at 661.org
Mon May 16 22:25:48 UTC 2016
On Mon, 16 May 2016, Andrea Del Signore wrote:
> > I've been knocking my head against a wall for more than a year trying to
> > figure out how to correctly mix two streams of audio while using
> > libsndfile for input and libao for output. My main requirement is that
> > I cannot assume anything about the output drivers -- that is, I cannot
> > depend on the output driver (ALSA, OSS, Sun, etc) being able to do the
> > mixing for me. Many of my target platforms lack any sort of mixing
> > services. I need to do this myself. I tried starting a mixer/player
> > thread that would work in a producer/consumer relationship with one or
> > two audio file decoder threads. I can play one sound at a time just
> > fine. When I try to do both, I get distortion followed by a segfault.
> not sure if I understood correctly: do you just want to mix N files?
> Like you I'm learning libsndfile and libao so this is my attempt to mix some audio files:
> Can someone explain line 88 (I already read the sndfile FAQ)?
I'm not simply trying to mix two files. My main project is a game engine
in which two sounds are allowed at any one time. For instance, there can
be constant background music punctuated by sound effects. I can't get
these to mix correctly.
Regarding your line 88, I had trouble with this too:
sf_count_t item_read = sf_read_float (sndfile[i], filebuffer, BUFFSIZE);
// WHY BUFFSIZE? Shouldn't be BUFFSIZE * channels?
The third parameter is for the number of items or frames. A frame is made
up of one sample per channel. Earlier you set up filebuffer like this:
buflen = BUFFSIZE * sf_info.channels;
filebuffer = malloc(buflen * sizeof(float));
The size of filebuffer is BUFFSIZE float-sized frames. Therefore when you
specify BUFFSIZE as the number of floats to read, they all fit in
dave at 661.org
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